In order to meet the increasing demand for wireless data traffic since the commercialization of 4th generation (4G) communication systems, the development focus is on the 5th generation (5G) or pre-5G communication system. For this reason, the 5G or pre-5G communication system is called a beyond 4G network communication system or post long-term evolution (LTE) system. Implementation of the 5G communication system in millimeter wave (mmWave) frequency bands (e.g., 60 GHz bands) is being considered to accomplish higher data rates. In order to increase the propagation distance by mitigating propagation loss in the 5G communication system, discussions are underway about various techniques such as beamforming, massive multiple-input multiple output (MIMO), full dimensional MIMO (FD-MIMO), array antenna, analog beamforming, and large-scale antenna. Also, in order to enhance network performance of the 5G communication system, developments are underway of various techniques such as evolved small cell, advanced small cell, cloud radio access network (RAN), ultra-dense network, device-to-device (D2D) communication, wireless backhaul, moving network, cooperative communication, coordinated multi-points (CoMP), and interference cancellation. Furthermore, the ongoing research includes the use of hybrid frequency shift keying (FSK) and quadrature amplitude modulation (QAM){FQAM} and sliding window superposition coding (SWSC) as advanced coding modulation (ACM), filter bank multi-carrier (FBMC), non-orthogonal multiple access (NOMA), and sparse code multiple access (SCMA).
Meanwhile, the Internet is evolving from a human-centric communication network in which information is generated and consumed by humans to the Internet of things (IoT) in which distributed things or components exchange and process information. The combination of the cloud server-based Big data processing technology and the IoT begets Internet of everything (IoE) technology. In order to secure the sensing technology, wired/wireless communication and network infrastructure, service interface technology, and security technology required for implementing the IoT, recent research has focused on sensor network, machine-to-machine (M2M), and machine-type communication (MTC) technologies. In the IoT environment, it is possible to provide an intelligent Internet Technology that is capable of collecting and analyzing data generated from connected things to create new values for human life. The IoT can be applied to various fields such as smart home, smart building, smart city, smart car or connected car, smart grid, health care, smart appliance, and smart medical service through legacy information technology (IT) and convergence of various industries.
Thus, there are various attempts to apply the IoT to the 5G communication system. For example, the sensor network, M2M, and MTC technologies are implemented by means of the 5G communication technologies such as beamforming, MIMO, and array antenna. The application of the aforementioned cloud RAN as a big data processing technology is an example of convergence between the 5G and IoT technologies.
One of the main design goals of the 5G communication system is to provide communication throughput to cope with explosive data growth. To achieve this goal, research is mainly being conducted into aspects of massive bandwidth, small cell, and next generation transmission schemes. In order to secure a massive bandwidth, exploiting licensed band above 6 GHz in addition to the currently in use licensed band below 6 GHz and unlicensed/shared band are being considered. It may also be possible to increase spatial reuse in a given bandwidth with the introduction of the small cell concept.
Meanwhile, a 5G communication system should be designed to support IoT services and high-reliability/low-delay communication services as well as legacy mobile communication services. It may also be necessary consider future compatibility for service expansion, i.e., for supporting services expected in the future, without change of network infrastructure including base stations.
In LTE, as one of the representative 4G communication standards, the capacity of a transmission/reception link is determined as follows. A terminal (user equipment (UE)) performs measurement on a reference signal transmitted by a base station (evolved Node B (eNB)) in downlink and reports signal quality to the base station. Examples of the reference signal may include common/cell-specific reference signal (CRS), discovery reference signal (DRS), and channel state information-reference signal (CSI-RS), which are received by all UEs within a cell, and dedicated/demodulation reference signal (DMRS), which is received by a specific UE. The UE may observe/measure CRS/DRS/CSI-RS periodically or aperiodically and transmit, under the control of the eNB, a channel quality indicator (CQI) indicative of the measured channel quality to the eNB. The UE may use an uplink control channel for a periodic measurement report or an uplink data channel for an aperiodic measurement report. The eNB schedules the UE by allocating physical channel resource blocks based on the CQI transmitted by the UE and transmits resource allocation information as the scheduling result to the UE. The resource allocation information is conveyed in a physical downlink control channel (PDCCH) in the form of a control signal scrambled with a cell radio network temporary identifier (C-RNTI) or multimedia broadcast/multicast service (MBMS) radio network temporary identifier (M-RNTI), and the UE may receive on the physical channel block allocated in a physical downlink shared channel (PDSCH) indicated in the control signal.
In uplink, the eNB may performs measurement on a reference signal transmitted by the UE to determine signal quality. Examples of the reference signal of the UE uses a sounding reference signal (SRS) being periodically allocated (about 2˜320 ms) by the eNB. Although not specific in the current standards, it may also be possible to consider using DMRS that is transmitted along with data being transmitted by the UE in uplink. The eNB may schedule the UE by allocating physical channel resource blocks based on the CQI generated as a result of measurement on the reference signal transmitted by the UE and transmit allocation information to the UE. The allocation information is conveyed in a physical downlink control channel (PDCCH) in the form of a control signal scrambled with a C-RNTI or M-RNTI, and the UE transmits the physical channel resource blocks in a physical uplink shared channel (PUSCH) indicated by the control channel.
LTE supports two different duplex modes: frequency division duplex (FDD) and time division duplex (TDD). In order to cope with traffic fluctuation and traffic amount reversion between downlink and uplink, it may be more appropriate to employ adoption of TDD for 5G communication systems from an economic view point because TDD makes it possible to implement both downlink and uplink in one carrier. Resource ratio of downlink and uplink should be changeable dynamically.
Meanwhile, deploying small cell eNBs close to each other in consideration of interference therebetween may increase costs. Also, in order to use unlicensed/shared band, it is necessary to take into consideration coexistence with other system/operator devices. In this respect, there is a need to consider interference control and a resource access scheme among the small cell eNBs.
Furthermore, there is a need of an improved resource access method for covering various service characteristics.